CN109390584A - 负电极与锂电池 - Google Patents
负电极与锂电池 Download PDFInfo
- Publication number
- CN109390584A CN109390584A CN201810900059.4A CN201810900059A CN109390584A CN 109390584 A CN109390584 A CN 109390584A CN 201810900059 A CN201810900059 A CN 201810900059A CN 109390584 A CN109390584 A CN 109390584A
- Authority
- CN
- China
- Prior art keywords
- pvdf
- phase
- lithium
- polyvinylidene fluoride
- negative electrode
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 76
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 70
- 229920002981 polyvinylidene fluoride Polymers 0.000 claims abstract description 161
- 239000002033 PVDF binder Substances 0.000 claims abstract description 159
- 239000000463 material Substances 0.000 claims abstract description 32
- 239000003792 electrolyte Substances 0.000 claims abstract description 16
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 25
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 15
- 229910002804 graphite Inorganic materials 0.000 claims description 15
- 239000010439 graphite Substances 0.000 claims description 15
- 239000011149 active material Substances 0.000 claims description 13
- 238000000919 Fourier transform infrared map Methods 0.000 claims description 10
- 239000010949 copper Substances 0.000 claims description 7
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 6
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 239000004411 aluminium Substances 0.000 claims description 3
- 229910052782 aluminium Inorganic materials 0.000 claims description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 229910052710 silicon Inorganic materials 0.000 claims description 3
- 239000010703 silicon Substances 0.000 claims description 3
- 229910001220 stainless steel Inorganic materials 0.000 claims description 3
- 239000010935 stainless steel Substances 0.000 claims description 3
- 229910002986 Li4Ti5O12 Inorganic materials 0.000 claims 2
- 238000012360 testing method Methods 0.000 description 37
- 230000004087 circulation Effects 0.000 description 32
- 239000011889 copper foil Substances 0.000 description 21
- 238000000151 deposition Methods 0.000 description 20
- 230000008021 deposition Effects 0.000 description 20
- FXHOOIRPVKKKFG-UHFFFAOYSA-N N,N-Dimethylacetamide Chemical compound CN(C)C(C)=O FXHOOIRPVKKKFG-UHFFFAOYSA-N 0.000 description 14
- 238000000576 coating method Methods 0.000 description 14
- 210000001787 dendrite Anatomy 0.000 description 14
- 239000011248 coating agent Substances 0.000 description 12
- 239000003990 capacitor Substances 0.000 description 11
- 229940113088 dimethylacetamide Drugs 0.000 description 10
- 230000005611 electricity Effects 0.000 description 10
- 238000002360 preparation method Methods 0.000 description 9
- 238000002955 isolation Methods 0.000 description 7
- 229910004764 HSV900 Inorganic materials 0.000 description 5
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 5
- 210000004027 cell Anatomy 0.000 description 5
- 239000011888 foil Substances 0.000 description 5
- 229910001416 lithium ion Inorganic materials 0.000 description 5
- 229910021382 natural graphite Inorganic materials 0.000 description 5
- 238000001228 spectrum Methods 0.000 description 5
- 238000004458 analytical method Methods 0.000 description 4
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 4
- 239000007784 solid electrolyte Substances 0.000 description 4
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 description 3
- 238000005033 Fourier transform infrared spectroscopy Methods 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- -1 ether compound Chemical class 0.000 description 3
- 229910003473 lithium bis(trifluoromethanesulfonyl)imide Inorganic materials 0.000 description 3
- QSZMZKBZAYQGRS-UHFFFAOYSA-N lithium;bis(trifluoromethylsulfonyl)azanide Chemical compound [Li+].FC(F)(F)S(=O)(=O)[N-]S(=O)(=O)C(F)(F)F QSZMZKBZAYQGRS-UHFFFAOYSA-N 0.000 description 3
- 238000011068 loading method Methods 0.000 description 3
- 239000012528 membrane Substances 0.000 description 3
- 238000012876 topography Methods 0.000 description 3
- 238000012546 transfer Methods 0.000 description 3
- WNXJIVFYUVYPPR-UHFFFAOYSA-N 1,3-dioxolane Chemical compound C1COCO1 WNXJIVFYUVYPPR-UHFFFAOYSA-N 0.000 description 2
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 2
- LCGLNKUTAGEVQW-UHFFFAOYSA-N Dimethyl ether Chemical compound COC LCGLNKUTAGEVQW-UHFFFAOYSA-N 0.000 description 2
- 229910001290 LiPF6 Inorganic materials 0.000 description 2
- 239000004743 Polypropylene Substances 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 230000007812 deficiency Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 description 2
- 229910003002 lithium salt Inorganic materials 0.000 description 2
- 159000000002 lithium salts Chemical class 0.000 description 2
- CPABIEPZXNOLSD-UHFFFAOYSA-N lithium;oxomanganese Chemical compound [Li].[Mn]=O CPABIEPZXNOLSD-UHFFFAOYSA-N 0.000 description 2
- 229920001155 polypropylene Polymers 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- ZXMGHDIOOHOAAE-UHFFFAOYSA-N 1,1,1-trifluoro-n-(trifluoromethylsulfonyl)methanesulfonamide Chemical compound FC(F)(F)S(=O)(=O)NS(=O)(=O)C(F)(F)F ZXMGHDIOOHOAAE-UHFFFAOYSA-N 0.000 description 1
- NPNPZTNLOVBDOC-UHFFFAOYSA-N 1,1-difluoroethane Chemical compound CC(F)F NPNPZTNLOVBDOC-UHFFFAOYSA-N 0.000 description 1
- VAYTZRYEBVHVLE-UHFFFAOYSA-N 1,3-dioxol-2-one Chemical compound O=C1OC=CO1 VAYTZRYEBVHVLE-UHFFFAOYSA-N 0.000 description 1
- 125000006091 1,3-dioxolane group Chemical class 0.000 description 1
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 1
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 1
- 229910000552 LiCF3SO3 Inorganic materials 0.000 description 1
- PFYQFCKUASLJLL-UHFFFAOYSA-N [Co].[Ni].[Li] Chemical compound [Co].[Ni].[Li] PFYQFCKUASLJLL-UHFFFAOYSA-N 0.000 description 1
- CQBLUJRVOKGWCF-UHFFFAOYSA-N [O].[AlH3] Chemical compound [O].[AlH3] CQBLUJRVOKGWCF-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 238000000627 alternating current impedance spectroscopy Methods 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 235000019241 carbon black Nutrition 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- SIXOAUAWLZKQKX-UHFFFAOYSA-N carbonic acid;prop-1-ene Chemical compound CC=C.OC(O)=O SIXOAUAWLZKQKX-UHFFFAOYSA-N 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- 239000006184 cosolvent Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 150000005676 cyclic carbonates Chemical class 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000005518 electrochemistry Effects 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- RTZKZFJDLAIYFH-UHFFFAOYSA-N ether Substances CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 1
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000002241 glass-ceramic Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000011244 liquid electrolyte Substances 0.000 description 1
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 1
- 229910001540 lithium hexafluoroarsenate(V) Inorganic materials 0.000 description 1
- MHCFAGZWMAWTNR-UHFFFAOYSA-M lithium perchlorate Chemical compound [Li+].[O-]Cl(=O)(=O)=O MHCFAGZWMAWTNR-UHFFFAOYSA-M 0.000 description 1
- 229910001486 lithium perchlorate Inorganic materials 0.000 description 1
- 229910001496 lithium tetrafluoroborate Inorganic materials 0.000 description 1
- VGYDTVNNDKLMHX-UHFFFAOYSA-N lithium;manganese;nickel;oxocobalt Chemical compound [Li].[Mn].[Ni].[Co]=O VGYDTVNNDKLMHX-UHFFFAOYSA-N 0.000 description 1
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 1
- URIIGZKXFBNRAU-UHFFFAOYSA-N lithium;oxonickel Chemical compound [Li].[Ni]=O URIIGZKXFBNRAU-UHFFFAOYSA-N 0.000 description 1
- 229920002521 macromolecule Polymers 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 239000004745 nonwoven fabric Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 229920000098 polyolefin Polymers 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
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Abstract
一种锂电池,包括:正电极;负电极;以及电解质,位于正电极与负电极之间;其中,负电极包括:集电材,以及β相为主的聚偏二氟乙烯层,披覆于集电材上。β‑PVDF层的厚度介于1~10μm之间。
Description
技术领域
本发明属于锂电池技术领域,具体涉及一种锂电池负电极的层状结构与组成。
背景技术
可充电的电池需具有能量密度高、使用寿命长、安全性高、成本低等特性。锂金属负极被视作锂离子电池负极的有力候选,因为其具有低电化学电位(-3.04V vs.SHE)与极高的理论电容值(3860mAh/g)。然而在1980年代末期,因安全考虑而将锂金属电池取代为具有石墨负极的锂离子电池。锂金属负极的主要挑战为金属基板上的锂枝晶,其会降低库仑效率、体积膨胀、加速电解质分解、甚至穿透隔离膜造成短路与热失控。上述锂枝晶问题不只存在于锂金属负极,现行的石墨负极在过度充电或快速充电(大电流)的情形下,也可能沉积于负极上而形成锂枝晶。
综上所述,目前亟需新的负极结构以避免产生锂枝晶。
发明内容
本发明一实施例提供一种负电极,包括:集电材,以及β相为主的聚偏二氟乙烯层,披覆于集电材上。
本发明一实施例提供一种锂电池,包括:正电极;负电极;以及电解质,位于正电极与负电极之间,其中负电极包括:集电材,以及β相为主的聚偏二氟乙烯层,披覆于集电材上。
附图说明
图1为本发明实施例中负电极的示意图;
图2A为本发明实施例中β-PVDF层的表面形貌;
图2B为本发明实施例中β-PVDF层的顶部形貌与底部形貌;
图2C为本发明实施例中α-PVDF层与β-PVDF层的FTIR图谱;
图2D为本发明实施例中α-PVDF层与β-PVDF层的XRD图谱;
图3A为本发明实施例中沉积锂于铜工作电极上之后的SEM图;
图3B为本发明实施例中以不同电容负载沉积锂于β-PVDF@Cu工作电极上之后的SEM图;
图3C为本发明实施例中以不同电流密度沉积锂于β-PVDF@Cu工作电极上之后的SEM图;
图4A为本发明实施例中多次循环测试后的不同电池的库仑效率;
图4B为本发明实施例中多次循环测试后的不同电池的电压迟滞;
图4C为本发明实施例中采用β-PVDF@Cu工作电极的电池在多次循环测试后的电压对电容曲线;
图4D为本发明实施例中不同电池在不同电流密度的循环测试后的库仑效率;
图4E为本发明实施例中采用β-PVDF@Cu工作电极的电池在多次循环测试后的库仑效率以及电压对循环时间的折线;
图5A为本发明实施例中采用β-PVDF@Cu工作电极的电池在多次循环测试后的电化学交流阻抗图谱;
图5B为本发明实施例中循环测试前与循环测试后的β-PVDF层得FTIR图谱;
图5C为本发明实施例中循环测试后的β-PVDF层的SEM图;
图6A为本发明实施例中不同电池在多次循环测试后的库仑效率;
图6B为本发明实施例中采用β-PVDF@Cu负极的电池在多次循环测试后的电压对电容曲线;
图6C为本发明实施例中采用β-PVDF@Li负极的电池在多次循环测试后的电压对电容曲线;
图7A为本发明实施例中不同电池经不同电流密度的多次循环测试后的电容量维持率;
图7B为本发明实施例中不同电池以不同电流密度进行充放电的台阶电压;
图7C为本发明实施例中不同电池的充放电曲线;
图7D为本发明实施例中采用β-PVDF@Li负极在多次循环测试后的电容与库仑效率;
图8A为本发明实施例中天然石墨的SEM图;
图8B为本发明实施例中β-PVDF@NG的SEM图;
图9A为本发明实施例中采用天然石墨负极的电池于多次循环测试后的电压对电容曲线;
图9B为本发明实施例中采用β-PVDF@NG负极的电池在多次循环测试后的电压对电容曲线;
图9C为本发明实施例中不同电池在多次循环测试后的库仑效率;
图10A为本发明实施例中循环测试后的天然石墨负极的SEM图;
图10B为本发明实施例中循环测试后的β-PVDF@NG负极的SEM图;
图11A为本发明实施例中采用β-PVDF@NG负极的电池经过度锂化及多次循环测试后的库仑效率;
图11B为本发明实施例中采用β-PVDF@NG负极的电池经过度锂化及多次循环测试后的电容;
图12为本发明实施例中不同厂牌β-PVDF层的FTIR图谱;
【附图标记说明】
SEI-固态电解质界面; 11-集电材;
13-活性物质; 15-β-PVDF层;
100-负电极。
具体实施方式
图1为本发明实施例中的负电极的示意图,如图1所示,负电极100包括集电材11,以及披覆于集电材11上的β相为主的聚偏二氟乙烯(β-PVDF)层15。以β-PVDF层15的FTIR图谱中,840cm-1的信号强度作为β相的PVDF的信号强度,将764cm-1的信号强度作为α相的PVDF的信号强度,β相与α相的信号强度比例介于70∶30至95∶5之间。β-PVDF层15在电池充电时可提供通道,使电解质中的锂离子沉积于集电材11与β-PVDF层15之间形成固态电解质界面SEI。固态电解质界面SEI有利于电池在多次充放电循环后维持其库仑效率,且因β-PVDF层15的存在不会产生锂枝晶。
在本发明的一些实施例中,β-PVDF层15的厚度为1~10μm。若β-PVDF层15的厚度过薄,则无法抑制锂枝晶形成。若β-PVDF层15的厚度过厚,则会增加锂离子穿过β-PVDF层15的电阻,进而增加充电/放电的极化率。在本发明的一实施例中,集电材11包括锂、铜、铝、镍、不锈钢或石墨。
在本发明的一些实施例中,负电极100还包括活性物质13,在集电材11与β-PVDF层15之间,且活性物质13的材料不同于集电材11的材料。举例来说,活性物质13包括石墨、硅、Li4TisO12或锂金属。在本发明的一实施例中,集电材11为铜箔,而活性物质13可为锂层。在本发明的一些实施例中,集电材11为铜箔,而活性物质13可为石墨颗粒。
在本发明的一些实施例中,上述负电极100可搭配正电极,并将电解质设置于负电极100与正电极之间,以形成锂电池。在本发明的一些实施例中,可进一步在正电极与负电极100之间夹设隔离膜(如聚烯烃)。实验证明,具有负电极100的锂电池比一般负电极(不具有β-PVDF层披覆集电材)在多次充放电循环后,具有较佳的库仑效率与稳定性。在本发明的一些实施例中,电解质根据形态可分为液态、胶态与固态。液态电解质由锂盐、溶剂或离子液体所组成,常用的锂盐有LiPF6、LiAsF6、LiClO4、LiBF4、LiTFSI或LiCF3SO3等,常用的溶剂有环状碳酸酯(如碳酸乙烯酯、碳酸丙烯酯)、链状碳酸酯(如碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯)、醚类化合物(如二甲醚、1,3-二氧环戊烷)等。固态电解质分为高分子及玻璃陶瓷等。在本发明的一些实施例中,正极材料包含磷酸锂铁、锂钴氧、锂镍氧、锂锰氧、锂镍钴铝氧、锂镍钴锰氧(三元)或富锂锰氧等。
为了提高锂电池的整体电容量,正负极的容量都必须要提升,现今正极容量已由原本的170mAh/g提升至190-200mAh/g,且正极的高库仑效率与可逆性确保了其容量提升,有效提高电池能量密度。然而现今的石墨负极容量360mAh/g,若使用锂金属做为负极可提升至3000mAh/g,但枝晶与库仑效率严重限制了其应用。当集电材11或活性物质13为碳材如石墨时,可在其表面披覆高分子膜,可有效抑制枝晶。因此,当过度锂化20%时,即可让石墨电极提升到432mAh/g,可以有效提升电池容量并确保可逆性。
为使本发明的目的、技术方案和优点更加清楚明白,以下结合具体实施例,并参照附图,对本发明作进一步的详细说明。
实施例
制备例1(β-PVDF@Cu)
在室温下将聚偏二氟乙烯(PVDF,购自ArkemaInc的 HSV900)溶于二甲基乙酰胺(DMAC),形成10wt%的PVDF溶液。用自动刮刀涂布机(购自Allreal的B0100)将上述PVDF溶液涂到15μm厚的铜箔上,再放置于加热板上加热至65℃并维持90分钟,以除去涂层中的DMAC并确保形成的PVDF层为β相。上述β相的PVDF层厚度为约4μm。将具有β相的PVDF上的铜箔压切成直径13mm的碟状物。经SEM分析可知,上述β相的PVDF层的表面形貌具有相连的微米尺寸半球,如图2A所示。从铜箔剥下β相的PVDF层后,虽然其顶部表面有孔洞,但其底部表面没有孔洞,如图2B所示。β相的PVDF层的底部形貌与铜箔表面的图案吻合,显示β相的PVDF层与铜箔之间紧密贴合。上述β相的PVDF层的FTIR图谱如图2C所示,而XRD图谱如图2D所示。
制备例2(α-PVDF@Cu)
在室温下将聚偏二氟乙烯(PVDF,购自ArkemaInc的 HSV900)溶于二甲基乙酰胺(DMAC),形成10wt%的PVDF溶液。用自动刮刀涂布机(购自Allreal的B0100)将上述PVDF溶液涂布到15μm厚的铜箔上,再放入快速空气对流机中加热至70℃快速干燥涂层,除去涂层中的DMAc并确保形成的PVDF层主要为α相。上述α相的PVDF层厚度约4μm。将具有α相的PVDF层上的铜箔压切成直径13mm的碟状物。上述α相的PVDF层的FTIR图谱如图2C所示,XRD图谱如图2D所示。如图2C的FTIR图谱所示,β相的PVDF层具有840cm-1与510cm-1的强吸收峰,而α相的PVDF层具有764cm-1、614cm-1与532cm-1的强吸收峰。如图2D的XRD图谱所示,β相的PVDF层在2θ=20.26°有信号表征,而α相的PVDF层在2θ=17.66°、18.30°及19.90°有信号表征。以FTIR图谱中840cm-1的信号强度作为β相的PVDF的信号强度,将764cm-1的信号强度作为α相的PVDF的信号强度,并计算上述PVDF膜中β相与α相的信号强度比例。上述α相的PVDF层中,α相信号(764cm-1)占48.7%,而β相信号(840cm-1)占51.3%。
实施例1
取15μm厚的铜箔作为工作电极,取锂箔作为对向电极。将市售的聚丙烯(Celgard2400)夹设于工作电极与对向电极之间作为隔离膜,并用聚丙烯围绕上述结构后放入电池外壳中。取双三氟甲烷磺酰亚胺锂(LiTFSI)溶于1,3-二氧戊环(DOL)与1,2-二甲氧基乙烷(DME)的共溶剂(v/v=1/1)中以形成1M的LiTFSI溶液,且上述溶液添加3wt%的硝酸锂形成电解质。将电解质填入工作电极与对向电极之间的空间,以形成CR2032型的钮扣型电池。通过施加0.5mAhcm-2、2mAhcm-2与4mAhcm-2的电容负载(电流密度为1mAcm-2)沉积固定量的锂至工作电极上。在低电容负载(0.5mAhcm-2与2mAhcm-2)时,上述沉积在工作电极上的锂具有针状凸起结构的粗糙表面。在高电容负载(4mAhcm-2)时,上述沉积于工作电极上的锂具有巨大枝晶聚集(尺寸达几百微米)的草毯状粗糙表面。上述结构如图3A所示。
在施加0.5mAhcm-2、2mAhcm-2与4mAhcm-2的电容负载(电流密度为1mAcm-2)沉积固定量的锂到工作电极上后,施加1V的反向电压脱除工作电极上的锂,完成循环测试。循环稳定性可由库仑效率表示,其定义为每一循环中,脱除锂与沉积锂的比例。如图4A所示,每一循环中沉积锂的电容负载为0.5mAhcm-2,而电流密度为1mAcm-2。采用铜箔工作电极的电池其库仑效率散乱,且在约90次循环后大幅降低。采用铜箔工作电极的电池其电压迟滞(锂沉积与剥除之间的电压差异)从31mV大幅增加到80mV(见图4B),与其库仑效率快速降低的现象一致。
如图4D所示,每一循环中沉积锂的电容负载为0.5mAhcm-2,而电流密度分别为2mAcm-2及5mAcm-2。高电流密度会导致不需要的锂枝晶成长,采用铜箔工作电极的电池其库仑效率散乱程度随着电流密度提高,原因在于电极-电解质的界面不稳定。
实施例2
与实施例1类似,不同之处仅在于将15μm厚的铜箔置换为制备例1的碟状样品(β-PVDF@Cu)。其他对向电极、隔离膜、电解质与钮扣型电池的结构均与实施例1相同。通过施加0.5mAhcm-2、2mAhcm-2与4mAhcm-2的沉积电容负载(电流密度为1mAcm-2)沉积固定量的锂至工作电极上,接着施加1V的反向电压脱除工作电极上的锂,完成循环测试。在所有的电容负载中,上述沉积在工作电极上的锂均具有平滑表面,且其剖面结构依序为β-PVDF层的顶层、锂的致密沉积物的中间层、与铜箔的底层。锂中间层的厚度落在理论值的范围中。举例来说,当电容负载为2mAhcm-2时,锂中间层的厚度约10μm。值得注意的是,β-PVDF层的厚度仅为锂中间层厚度的一小部份。举例来说,当电容负载为4mAhcm-2时,β-PVDF层的厚度为锂中间层的厚度的20%。上述结构如图3B所示。β-PVDF层的完整型态,表示其可挠性与机械强度足以承受巨大的体积变化。即使在高电流密度如2~5mAcm-2下(电容负载为2mAhcm-2),β-PVDF@Cu工作电极上仍具有平滑的表面构形而无枝晶,如图3C所示。
在施加0.5mAhcm-2、2mAhcm-2与4mAhcm-2的电容负载(电流密度为1mAcm-2)沉积固定量的锂至工作电极上后,施加1V的反向电压脱除工作电极上的锂,完成循环测试。循环稳定性可由库仑效率表示,其定义为每一循环中,脱除锂与沉积锂的比例。如图4A所示,每一循环中沉积锂的电容负载为0.5mAhcm-2,而电流密度为1mAcm-2。采用β-PVDF@Cu工作电极的电池的库仑效率在约10次循环内约98%,且在200次循环后维持稳定。采用β-PVDF@Cu工作电极的电池在多次循环后,其电压迟滞稳定维持在33mV(如图4B所示),且电压曲线不变(如图4C所示)。β-PVDF层可在电极与电解质之间产生超稳定的界面。
如图4D所示,每一循环中沉积锂的电容负载为0.5mAhcm-2,而电流密度分别为2mAcm-2及5mAcm-2。在图4D中,采用β-PVDF@Cu工作电极的电池其稳定的库仑效率(分别为96.5%及92.5%),明显优于采用铜箔工作电极的电池其库仑效率。
如图4E所示,每一循环中沉积锂的电容负载为2mAhcm-2,而电流密度分别为1mAcm-2。采用β-PVDF@Cu工作电极的电池经长时间循环后,仍具有稳定的库仑效率。即使电容负载增加至2mAhcm-2,β-PVDF@Cu工作电极在1mAcm-2的电流密度下循环超过250次后的平均库仑效率仍高达98.7%(高稳定循环效能),如图4E所示。图4E中的平滑电压曲线亦表示循环中的稳定动力学。
在频率为100kHz~0.1Hz且振幅为10mV时,用频率分析仪(购自MetrohmAutolab的PGSTAT30)取得开路电压的电化学阻抗图谱。交流阻抗分析可确认多次循环(每一循环中沉积锂的电容负载为2mAhcm-2,而电流密度为1mAcm-2)后,采用β-PVDF@Cu工作电极的电池仍维持低电荷转移电阻,如图5A所示。上述循环重复250次后,从电池取下β-PVDF层进行后续分析,确认β-PVDF层的化学与机械性质是否改变。循环测试前与循环测试后的β-PVDF层的FTIR图谱如图5B所示,证明循环测试后的β-PVDF层化学结构不变。循环测试后的β-PVDF层的SEM分析如图5C所示,证明循环测试后的β-PVDF层的微结构不变。
实施例3
与实施例1类似,不同之处仅在于将15μm厚的铜箔置换为制备例2的碟状样品(α-PVDF@Cu)。其他对向电极、隔离膜、电解质与钮扣型电池的结构均与实施例1相同。
在施加0.5mAhcm-2、2mAhcm-2与4mAhcm-2的电容负载(电流密度为1mAcm-2)沉积固定量的锂至工作电极上后,施加1V的反向电压脱除工作电极上的锂,完成循环测试。循环稳定性可由库仑效率表示,其定义为每一循环中,脱除锂与沉积锂的比例。如图4A所示,每一循环中沉积锂的电容负载为0.5mAhcm-2,而电流密度为1mAcm-2。采用α-PVDF@Cu工作电极的电池其库仑效率在前50次循环中,低于采用铜箔工作电极的电池与采用β-PVDF@Cu工作电极的电池的库仑效率。虽然采用α-PVDF@Cu工作电极的电池的库仑效率在多次循环后逐渐提高,但其电压迟滞仍高于采用β-PVDF@Cu工作电极的电池的电压迟滞,如图4B所示。这表示采用α-PVDF@Cu工作电极的电池具有实质上较高的总电荷转移电阻。由实施例2与3的比较可知,采用β-PVDF@Cu工作电极的电池比采用α-PVDF@Cu工作电极的电池的效能好,即PVDF层的极性很重要。
制备例3(β-PVDF@Li)
在室温下将聚偏二氟乙烯(PVDF,购自ArkemaInc的 HSV900)溶于二甲基乙酰胺(DMAc),形成10wt%的PVDF溶液。用自动刮刀涂布机(购自Allreal的B0100)将上述PVDF溶液涂至300μm厚、直径为16mm的锂箔上,再放置于填有氩气的干燥箱中加热至65℃并维持90分钟,接着在室温下抽真空隔夜,除去涂层中的DMAC并确保形成的PVDF层为β相。上述β相的PVDF层厚度约4μm。
LFP正极的制备方法如下:在NMP中混合20重量份的磷酸锂铁(购自AdvancedLithium Electrochemistry Co.,Ltd.)、2重量份的PVDF、1重量份的石墨片(购自TIMICAL的KS-6)与2重量份的碳黑(购自TIMICAL的super P),制备磷酸锂铁(LFP)正极,其质量负载约4.0mgcm-2。
取市售的碳酸酯溶液作为电解质,其包含溶于乙烯碳酸酯与二甲基碳酸酯(v/v=1/2)的LiPF6溶液(1.2M),且上述溶液添加4wt%的氟化乙烯碳酸酯。
取实施例2的β-PVDF@Cu作为负极,并预先在锂离子溶液中施加电容负载1mAhcm-2。处理后的β-PVDF@Cu负极搭配LFP正极,并将上述市售电解质加入正极与负极之间。上述电池在2.5V与3.8V之间循环。在电流密度为0.3C时,采用β-PVDF@Cu负极的电池其循环效能具有两阶段的稳定性,如图6A所示。在前四十次的循环中,采用β-PVDF@Cu负极的电池的电容衰退非常低(每一循环下降约0.11%),但之后的电容衰退非常快(每一循环下降约0.84%)。采用β-PVDF@Cu负极的电池在循环后的电压极化率(在0.3C,1C=170mAhg-1)无明显改变,表示其电荷转移电阻不变,如图6B所示。如此一来,四十次循环后的加速电容损失主要来自于负极的锂源不足而非界面的不稳定性。负极锂源不足的原因为负极的沉积/脱除的库仑效率不是100%。
取β-PVDF@Li作为负极,并搭配LFP正极。将上述市售电解质加入正极与负极之间,并进行相同的循环实验。由于β-PVDF@Li负极具有足够的锂源,采用其的电池在0.5C具有优异的可逆电容维持率。在两百次循环后的电池,其电容高于141mAhg-1,电容维持率为94.3%,且稳定的库仑效率为99.85%。采用β-PVDF@Li负极的电池的电压曲线显示其电压极化率改变小(在0.5C),如图6C所示。
取直径16mm的锂箔作为负极,并搭配LFP正极(质量负载为10.5mgcm-2)。另外取β-PVDF@Li作为负极,并搭配LFP正极(质量负载为10.5mgcm-2)。将上述市售电解质加入正极与负极之间,并进行相同的循环实验。如图7A所示,在0.1C至3C的电流密度的倍率效能测试中,采用锂箔负极的电池在较高电流密度(2C与3C)的循环电容较低。如图7B所示,采用锂箔负极的电池的电流极化率大于采用β-PVDF@Li负极的电池的电流极化率。以0.5C的电流密度进行充放电试验,上述两电池的充放电曲线如图7C所示。采用β-PVDF@Li负极的电池在多次循环后的电容与库仑效率如图7D所示。由上述可知,采用β-PVDF@Li负极的电池具有良好的倍率效能与电容维持率(100次循环后仍有100%)。
综上所述,薄层的β-PVDF可沉积无锂枝晶的锂层,并在高电流密度下改善循环效能。薄层的β-PVDF可确保锂负极的高能量与电容密度,且其涂布制程易于大量生产。
制备例4(β-PVDF@NG)
在室温下将聚偏二氟乙烯(PVDF,购自ArkemaInc的 HSV900)溶于二甲基乙酰胺(DMAc),形成10wt%的PVDF溶液。用自动刮刀涂布机(购自Allreal的B0100)将上述PVDF溶液涂至15μm厚的天然石墨电极上,再放置在加热板上加热至65℃并维持90分钟,除去涂层中的DMAC并确保形成的PVDF层为β相。上述β相的PVDF层厚度约4μm。未涂布PVDF的天然石墨电极的SEM照片如图8A所示,而β-PVDF@NG的SEM照片如图8B所示。在第8B图中,β-PVDF@NG具有一层状物均匀地披覆在天然石墨上,其应为β-PVDF层。
实施例4
与实施例1类似,不同之处仅在于将15μm厚的铜箔置换为无PVDF层的天然石墨电极。其他对向电极、隔离膜、电解质、与钮扣型电池的结构均与实施例1相同。以定电压对上述电池进行20%的过度锂化后,以0.2C的电流密度对上述电池进行充放电循环测试,如图9A所示。每次循环后的脱除锂容量越来越低,因此库仑效率降低。上述天然石墨电极在经过20%的过度锂化的充放电循环测试后,其SEM如图10A所示,明显有锂枝晶生长于表面上。
实施例5
与实施例1类似,不同之处仅在于将15μm厚的铜箔置换为制备例4的β-PVDF@NG。其他对向电极、隔离膜、电解质、与钮扣型电池的结构均与实施例1相同。以定电压对上述电池进行20%的过度锂化后,以0.2C的电流密度对上述电池进行充放电循环测试,如图9B所示。每次循环后的脱除锂容量越来越高,因此库仑效率增加。如图9C的比较可知,在多次循环测试后,采用β-PVDF@NG负极的电池其库仑效率远大于采用石墨负极的电池其库仑效率。上述β-PVDF@NG负极在经过20%的过度锂化的充放电循环测试后,其SEM如图10B所示,并无锂枝晶生长于表面上,证明β-PVDF层可抑制锂枝晶生长。
以定电压对上述电池进行20%、50%或100%的过度锂化后,以0.2C的电流密度对上述电池进行充放电循环测试,如图11A所示,不论过度锂化的程度为何,电池的库仑效率均可维持在95%以上。然而20%过度锂化的电池具有较佳的循环稳定度,如图11B所示。
制备例5(β-PVDF@Cu)
在室温下将购自不同厂牌的聚偏二氟乙烯(PVDF,购自ArkemaInc的HSV900与 HSV1800,购自Solvay的1300与6020,与购自TchnoAlpha Co.,Ltd.的ATROXTMHT900)分别溶于DMAC,形成10wt%的不同PVDF溶液。用自动刮刀涂布机(购自Allreal的B0100)将上述PVDF溶液分别涂到15μm厚的铜箔上,再放置于加热板上加热至65℃并维持90分钟,以除去涂层中的DMAC并确保形成的PVDF层为β相。上述β相的PVDF层的FTIR图谱如图12所示。以FTIR图谱中840cm-1的信号强度作为β相的信号强度,将764cm-1的信号强度作为α相的PVDF的信号强度,并计算上述PVDF膜中β相与α相的信号强度比例(I840/I764)如表1。
表1
以上所述的具体实施例,对本发明的目的、技术方案和有益效果进行了进一步详细说明,应理解的是,以上所述仅为本发明的具体实施例而已,并不用于限制本发明,凡在本发明的精神和原则之内,所做的任何修改、等同替换、改进等,均应包含在本发明的保护范围之内。
Claims (12)
1.一种负电极,其特征在于,包括:
一集电材,以及
一β相为主的聚偏二氟乙烯层,披覆于所述集电材上。
2.根据权利要求1所述的负电极,其特征在于,,所述β相为主的聚偏二氟乙烯层的厚度为1~10μm。
3.根据权利要求1所述的负电极,其特征在于,所述集电材包括锂、铜、铝、镍、不锈钢或石墨。
4.根据权利要求1所述的负电极,其特征在于,还包括一活性物质,位于所述集电材与所述β相为主的聚偏二氟乙烯层之间,且所述活性物质的材料不同于所述集电材的材料。
5.根据权利要求1所述的负电极,其特征在于,所述活性物质包括石墨、硅、Li4Ti5O12或锂金属。
6.根据权利要求1所述的负电极,其特征在于,β相为主的聚偏二氟乙烯层的FTIR图谱中,以840cm-1的信号强度作为β相的聚偏二氟乙烯的信号强度,以764cm-1的信号强度作为α相的聚偏二氟乙烯的信号强度,且β相的聚偏二氟乙烯与α相的聚偏二氟乙烯的信号强度比例介于70∶30至95∶5之间。
7.一种锂电池,其特征在于,包括:
一正电极;
一负电极;以及
一电解质,位于所述正电极与所述负电极之间,
其中,所述负电极包括:
一集电材,以及
一β相为主的聚偏二氟乙烯层,披覆于所述集电材上。
8.根据权利要求7所述的锂电池,其特征在于,所述β相为主的聚偏二氟乙烯层的厚度为1~10μm。
9.根据权利要求7所述的锂电池,其特征在于,所述集电材包括锂、铜、铝、镍、不锈钢或石墨。
10.根据权利要求7所述的锂电池,其特征在于,还包括一活性物质,位于所述集电材与所述β相为主的聚偏二氟乙烯层之间,且所述活性物质的材料不同于所述集电材的材料。
11.根据权利要求10所述的锂电池,其特征在于,所述活性物质包括石墨、硅、Li4Ti5O12或锂金属。
12.根据权利要求7所述的锂电池,其特征在于,β相为主的聚偏二氟乙烯层的FTIR图谱中,以840cm-1的信号强度作为β相的聚偏二氟乙烯的信号强度,以764cm-1的信号强度作为α相的聚偏二氟乙烯的信号强度,且β相的聚偏二氟乙烯与α相的聚偏二氟乙烯的信号强度比例介于70∶30至95∶5之间。
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